The present invention relates to a fan installation having at least one pole-changing asynchronous motor for driving the fan.
To maintain the temperature of the cooling water of an internal combustion engine (for instance a diesel engine) within a narrow range (about 5.degree. C.), the amount of air through the radiator, and thus the speed of rotation of the cooling fan, must be adjustable. Three-phase asynchronous motors are used to drive the fan due to their robustness. The fans are powered either from an auxiliary operating power supply or from a three-phase generator which is driven by the internal combustion engine which is to be cooled.
Fan installations having at least one pole-changing asynchronous motor for driving the fan are known in diesel electric locomotives. In such fan installations, several pole-changing asynchronous motors may be provided. The amount of air can then be varied by the switching a different number of fans on and off and/or by switching the poles of the fan drive motor. With, for instance, three two-step asynchronous motors, a six-step regulation of the speed of rotation is thus obtained. Due to the characteristic of the diesel engine and the different environmental conditions, changes in speed of rotation and thus switch-overs are frequently necessary.
A fan unit in which stepwise regulation of the speed of rotation is effected by pole changing of a two-step fan drive motor is known from French Patent Application FR-A-2 607 187. Within one step, the speed of rotation of the fan is substantially proportional to the speed of rotation of the combustion engine and thus proportional to the frequency of the generator feeding the fan drive motor, the generator being driven by the combustion engine. Within one step, continuous regulation of the fan drive motor is not possible.
U.S. Pat. No. 3,584,728 describes a control device for cranes, the characteristic of which, however, is very different from that of a fan drive. Thus, for example, in the case of crane drives, the power is substantially proportional to the speed of rotation of the drive motor, which in the case of fan installations, the output is proportional to the third power of the speed of rotation of the drive motor.
Furthermore, fan installations in which the non-pole-changing asynchronous motor is fed via a converter are known. In this way, the speed of rotation can be continuously regulated and the temperature of the cooling water thus kept within narrow limits, and the frequent switchings-over or switchings-on avoided. Unfortunately, these fan installations are very expensive.
In view of the numerous drawbacks of the known fan installations, there is a need to provide a fan installation in which the speed of rotation of the fan, and thus the amount of air, can be matched in simple manner to the amount of heat to be dissipated, in particular with the fewest possible switchovers or switchings-on.